The present invention relates generally to voice frame network systems such as Voice over Internet Protocol (VoIP) systems for concurrently carrying both voice and data signals. More particularly, it concerns method and apparatus for transitioning a high-speed data channel from voice mode to modem relay mode during session startup and establishing and maintaining synchronization of end-to-end modem de/compression.
VoIP is widely deployed by Internet Service Providers (ISPs) and within large or distributed private enterprises. Because voice channels require low latency for audio continuity and understanding in human conversation, typical VoIP implementations have utilized low-latency mechanisms such as Real-time Transfer Protocol (RTP). Unfortunately, the voice mode of VoIP channels that use RTP is an unreliable transport mechanism for high-speed modem signals. High packet drop rates and frequent retrains cause undesirable deterioration of the signal when high-speed modem signals are carried over a standard VoIP channel.